Many seismic investigation techniques have been developed. For the most part these investigations have been guided by three main sources of data: field seismic records, well logs, and laboratory measurements of ultrasonic pulse velocities in core samples of rock materials. With respect to ultrasonic pulse velocity measurements the travel time of an ultrasonic wavelet is measured between ends of a cylindrical or prismatic bar of rock material. The wavelength of the ultrasonic signal must be small compared to the length of the bar so that the wavelet has time to die out at the excitation end before it is detected at the receiving end. For samples of practical length the signal frequency must be of the order of hundreds of kHz. Seismic data are limited to frequencies below a few hundred hertz. Consequently the ultrasonic pulse velocity technique has not permitted measurements at frequencies approaching the seismic range.